Three taps A, B, and C can fill a tank in 12, 15, and 20 hours respectively. If tap A runs continuously while taps B and C operate alternately for one hour each, how long will it take to fill the tank completely?

Explanation

Tap A fills the tank at a rate of 1/12 per hour, tap B at 1/15 per hour, and tap C at 1/20 per hour. Since A runs continuously and B and C alternate each hour, calculating the combined filling rate over two hours and then determining the total time required shows that the tank will be filled in 7 hours.